Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
  • H05B45/37—Converter circuits
  • H05B45/3725—Switched mode power supply [SMPS]
  • H05B45/385—Switched mode power supply [SMPS] using flyback topology
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M3/00—Conversion of dc power input into dc power output
  • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
  • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
  • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
  • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
  • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
  • H02M3/33561—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having more than one ouput with independent control
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
  • H05B45/37—Converter circuits
  • H05B45/3725—Switched mode power supply [SMPS]
  • H05B45/382—Switched mode power supply [SMPS] with galvanic isolation between input and output
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
  • Y02B20/30—Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Definitions

• the present invention is directed generally to power control for driving LEDs. More particularly, various inventive methods and apparatus disclosed herein relate to drivers for LEDs comprising parallel flyback converters.
• LEDs light-emitting diodes
• Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others.
• Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications.
• Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g. red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects, for example, as discussed in detail in U.S. Patent Nos. 6,016,038 and 6,211,626.
• Flyback converters can be used for alternating current to direct current (AC/DC) conversion in driving light sources such as LEDs.
• One known flyback converter includes a flyback transformer, a metal-oxide semiconductor field effect transistor (MOSFET) and a snubber circuit.
• MOSFET metal-oxide semiconductor field effect transistor
• snubber circuit For greater output power requirements, known flyback converters require MOSFETs with greater voltage and current ratings. Higher voltage and current ratings, and therefore higher power ratings, result in MOSFETs with greater gate capacitance. Such transistors are comparatively expensive.
• high-current MOSFETs must be driven by circuits that have commensurately high power requirements.
• the comparatively high gate capacitance is difficult to drive.
• high power MOSFETs and required driver circuits are rather expensive.
• flyback transformers of flyback converters it is beneficial for the flyback transformers of flyback converters to have a comparatively low leakage inductance. As the power requirements of the flyback converter increase, the overall size of the flyback transformer increases and maintaining low leakage inductance is more difficult, if not impossible. Additionally, and among other drawbacks, flyback transformers for flyback converters having increased power handling capabilities are comparatively expensive and physically large. Thus, in addition to their cost, the high power flyback transformers require additional space.
• the present disclosure is directed to inventive methods and apparatuses comprising parallel AC/DC flyback converters for driving light sources (e.g., LEDs).
• the methods and apparatus of the present disclosure beneficially provide high output power and yet scalable from a comparatively low output power to a comparatively high output power, while providing comparatively high performance over a comparatively wide range of output power.
• the methods and apparatuses require comparatively low power MOSFETs and comparatively small flyback transformers.
• the desired output power can be achieved by selectively enabling the proper number of parallel flyback AC/DC converter stages to meet the demand of the output power.
• an apparatus for driving a light source is disclosed.
• the apparatus includes a first flyback AC/DC converter stage comprising a first switch, a first switch controller and a comparator; and a second flyback AC/DC converter stage comprising a second switch and a second switch controller, the second flyback AC/DC converter being electrically connected in parallel with the first flyback AC/DC converter stage.
• a method of driving a light source includes: sensing a voltage over a sense resistor in a first flyback AC/DC converter stage; comparing the voltage to a threshold voltage; and enabling a second flyback AC/DC converter stage if the voltage is greater than the threshold voltage.
• the apparatus includes a third flyback AC/DC converter comprising a third switch and a third switch controller.
• the third flyback AC/DC converter is electrically connected in parallel with the first flyback AC/DC converter and the second flyback AC/DC converter.
• the apparatus may further include a fourth flyback AC/DC converter comprising a fourth switch and a fourth switch controller.
• the fourth flyback AC/DC converter is electrically connected in parallel with the first flyback AC/DC converter, the second flyback AC/DC converter and the third flyback AC/DC converter.
• the method includes enabling a third flyback AC/DC converter stage if the voltage is greater than the threshold voltage after the enabling of the second AC/DC converter stage.
• the method includes enabling a fourth flyback AC/DC converter stage if the voltage is greater than the threshold voltage after the enabling of the third AC/DC converter stage.
• the method includes not enabling the second stage if the voltage is less than the threshold voltage.
• the method includes, after enabling the fourth flyback AC/DC converter stage, sensing the voltage over the sense resistor, and if the voltage is less than the threshold voltage, disabling the fourth flyback AC/DC converter stage. ln an embodiment, the method includes, after disabling the fourth flyback AC/DC converter stage, sensing the voltage over the sense resistor, and if the voltage is less than the threshold voltage, disabling the third flyback AC/DC converter stage.
• the method includes, after disabling the third flyback AC/DC converter stage, sensing the voltage over the sense resistor, and if the voltage is less than the threshold voltage, disabling the second flyback AC/DC converter stage.
• the term "LED” should be understood to include any electroluminescent diode or other type of carrier injection/junction- based system that is capable of generating radiation in response to an electric signal.
• the term LED includes, but is not limited to, various semiconductor-based structures that emit light in response to current, light emitting polymers, organic light emitting diodes (OLEDs), electroluminescent strips, and the like.
• LED refers to light emitting diodes of all types (including semi-conductor and organic light emitting diodes) that may be configured to generate radiation in one or more of the infrared spectrum, ultraviolet spectrum, and various portions of the visible spectrum (generally including radiation wavelengths from approximately 400 nanometers to approximately 700 nanometers).
• Some examples of LEDs include, but are not limited to, various types of infrared LEDs, ultraviolet LEDs, red LEDs, blue LEDs, green LEDs, yellow LEDs, amber LEDs, orange LEDs, and white LEDs (discussed further below).
• LEDs may be configured and/or controlled to generate radiation having various bandwidths (e.g., full widths at half maximum, or FWHM) for a given spectrum (e.g., narrow bandwidth, broad bandwidth), and a variety of dominant wavelengths within a given general color categorization.
• bandwidths e.g., full widths at half maximum, or FWHM
• FWHM full widths at half maximum
• an LED configured to generate essentially white light may include a number of dies which respectively emit different spectra of electroluminescence that, in combination, mix to form essentially white light.
• a white light LED may be associated with a phosphor material that converts electroluminescence having a first spectrum to a different second spectrum
• the term LED does not limit the physical and/or electrical package type of an LED.
• an LED may refer to a single light emitting device having multiple dies that are configured to respectively emit different spectra of radiation (e.g., that may or may not be individually controllable).
• an LED may be associated with a phosphor that is considered as an integral part of the LED (e.g., some types of white LEDs).
• light source should be understood to refer to any one or more of a variety of radiation sources, including, but not limited to, LED-based sources (including one or more LEDs as defined above), incandescent sources (e.g., filament lamps, halogen lamps), fluorescent sources, phosphorescent sources, high-intensity discharge sources (e.g., sodium vapor, mercury vapor, and metal halide lamps), lasers, other types of electroluminescent sources, pyro- luminescent sources (e.g., flames), candle-luminescent sources (e.g., gas mantles, carbon arc radiation sources), photo-luminescent sources (e.g., gaseous discharge sources), cathode luminescent sources using electronic satiation, galvano-luminescent sources, crystallo- luminescent sources, kine-luminescent sources, thermo-luminescent sources, triboluminescent sources, sonoluminescent sources, radioluminescent sources, and luminescent polymers.
• LED-based sources including one or more
• a given light source may be configured to generate electromagnetic radiation within the visible spectrum, outside the visible spectrum, or a combination of both.
• a light source may include as an integral component one or more filters (e.g., color filters), lenses, or other optical components.
• filters e.g., color filters
• lenses e.g., prisms
• light sources may be configured for a variety of applications, including, but not limited to, indication, display, and/or illumination.
• illumination source is a light source that is particularly configured to generate radiation having a sufficient intensity to effectively illuminate an interior or exterior space.
• sufficient intensity refers to sufficient radiant power in the visible spectrum generated in the space or environment (the unit “lumens” often is employed to represent the total light output from a light source in all directions, in terms of radiant power or "luminous flux”) to provide ambient illumination (i.e., light that may be perceived indirectly and that may be, for example, reflected off of one or more of a variety of intervening surfaces before being perceived in whole or in part).
• light fixture is used herein to refer to an implementation or arrangement of one or more lighting units in a particular form factor, assembly, or package.
• lighting unit is used herein to refer to an apparatus including one or more light sources of same or different types.
• a given lighting unit may have any one of a variety of mounting arrangements for the light source(s), enclosure/housing arrangements and shapes, and/or electrical and mechanical connection configurations. Additionally, a given lighting unit optionally may be associated with (e.g., include, be coupled to and/or packaged together with) various other components (e.g., control circuitry) relating to the operation of the light source(s).
• LED-based lighting unit refers to a lighting unit that includes one or more LED- based light sources as discussed above, alone or in combination with other non LED-based light sources.
• a “multi-channel” lighting unit refers to an LED-based or non LED-based lighting unit that includes at least two light sources configured to respectively generate different spectrums of radiation, wherein each different source spectrum may be referred to as a "channel" of the multi-channel lighting unit.
• controller is used herein generally to describe various apparatus relating to the operation of one or more light sources.
• a controller can be implemented in numerous ways (e.g., such as with dedicated hardware) to perform various functions discussed herein.
• a "processor” is one example of a controller which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform various functions discussed herein.
• a controller may be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions.
• controller components examples include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).
• a power factor controller PFC is implemented to control a plurality of flyback AC/DC converter stages.
• a processor or controller may be associated with one or more storage media (generically referred to herein as "memory,” e.g., volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM, floppy disks, compact disks, optical disks, magnetic tape, etc.).
• the storage media may be encoded with one or more programs that, when executed on one or more processors and/or controllers, perform at least some of the functions discussed herein.
• Various storage media may be fixed within a processor or controller or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or controller so as to implement various aspects of the present invention discussed herein.
• the terms "program” or "computer program” are used herein in a generic sense to refer to any type of computer code (e.g., software or microcode) that can be employed to program one or more processors or controllers.
• Fig. 1 illustrates a simplified schematic block diagram of a lighting system in accordance with a representative embodiment.
• FIG. 2 illustrates a conceptual diagram of enabling and disabling flyback AC/DC converter stages to provide a desired output power in accordance with a representative embodiment.
• FIG. 3 illustrates a simplified schematic diagram of a driver circuit comprising parallel flyback converter stages in accordance with a representative embodiment.
• Fig. 4 illustrates graphs of output power versus time, feedback voltage versus time, average sense voltage across a sense resistor, gate-to-source (Vgs) across a second MOSFET versus time, Vgs across a third MOSFET versus time, and Vgs across a fourth MOSFET versus time in accordance with a representative embodiment.
• Vgs gate-to-source
• Fig. 5 illustrates graphs of output power versus time, feedback voltage versus time, average sense voltage across a sense resistor, gate-to-source (Vgs) across a second MOSFET versus time, Vgs across a third MOSFET versus time, and Vgs across a fourth MOSFET versus time in accordance with a representative embodiment.
• Vgs gate-to-source
• Fig. 6 illustrates a flow-diagram of a method of driving a light source in accordance with a representative embodiment.
• the driver circuits of the representative embodiments comprise comparatively low power MOSFETs and comparatively small flyback transformers.
• various embodiments and implementations of the present invention are directed to methods and apparatus for driving light sources (e.g., LEDs) comprising a plurality of flyback AC/DC converters connected electrically in parallel.
• the desired output (DC) power can be achieved by selectively enabling the proper number of parallel flyback AC/DC converter stages to meet the demand of the output power.
• a lighting system 100 comprises a driver circuit 101 and a light source 102.
• the driver circuit 101 comprises a first flyback AC/DC converter stage 103, a second flyback AC/DC converter stage 104, a third flyback AC/DC converter stage 105, and a fourth flyback AC/DC converter stage 106.
• An AC input 107 is converted to a DC output 108 by the driver circuit 101; and the DC output 108 is provided to the light source 102.
• the flyback AC/DC converter stages 103-106 are connected electrically in parallel, and are selectively enabled/disabled based on the power/load requirements of the light source 102.
• the light source 102 illustratively comprises a plurality of LEDs, which are operable over a comparatively wide power range.
• the minimum output power provided to the light source 102 is approximately 0W and the maximum output power provided to the light source is approximately 200W.
• each of the flyback AC/DC converter stages 103-106 is configured to provide an output power in the range of approximately 0W to approximately 50 W. As described more fully herein, as more power is required by the light source 102, more flyback AC/DC converter stages are enabled to provide more power thereto.
• the number of flyback AC/DC converter staged enabled are reduced. It is emphasized that the maximum output power, the output power range of each flyback AC/DC converter stage and the number of flyback AC/DC converter stages are merely illustrative. The maximum output power, the output power range of each flyback AC/DC converter stage and the number of flyback AC/DC converter stages may each may be greater or less than the illustrative power and number of stages described in connection with the representative embodiment of Fig. 1. As will become clearer as the present description continues, the number of flyback AC/DC converter stages implemented in the driver circuit 101 governs the dynamic range of operational power of the light source 102.
• the maximum output power can be increased or decreased by increasing or decreasing the number of flyback AC/DC converter stages connected electrically in parallel.
• the implementation of four flyback AC/DC converter stages connected in parallel is merely illustrative, and the driver circuit 101 may comprise more or fewer than four flyback AC/DC converter stages connected in parallel.
• providing a plurality of flyback AC/DC converter stages reduces the power requirements of certain components of each flyback AC/DC converter stage, such as a switch (e.g., a MOSFET), and a flyback transformer.
• Fig. 2 illustrates a conceptual diagram of enabling and disabling flyback AC/DC converter stages in a driver circuit to provide a desired output power to a light source in accordance with a representative embodiment.
• the flyback AC/DC converter stages, the driver circuit and the light source may be as described above in connection with the representative embodiments of Fig. 1.
• the present example illustrates the function of driver circuit 101, comprising flyback AC/DC converter stages 103-106 connected in parallel, and providing power to light source 102.
• more or fewer flyback AC/DC converter stages may be implemented depending on the desired dynamic power range of the light source being driven by the driver circuit, and the limits of the each individual flyback AC/DC converter stage.
• flyback AC/DC converter stages 103-106 enabled increases.
• the process of enabling flyback AC/DC converter stages 103-106 is shown at side 201 of the conceptual diagram.
• the number of flyback AC/DC converter stages 103- 106 enabled decreases.
• the process of disabling the flyback AC/DC converter stages 103-106 is shown at side 202 of the conceptual diagram decreases. As there are four stages, there are four output power levels of operation.
• each of the flyback AC/DC converter stages 103-106 provides between 0W and 50W of output power to the light source 102, so the dymanic range of power provided to the light source 102 is approximately 0W to approximately 200W.
• Each of the flyback AC/DC converter stages 103- 106 is engaged based on the required output power, which is turn in governed by a respective threshold value.
• the threshold value is illustratively a threshold voltage across a sense resistor.
• a threshold current across a sense resistor can be used for the threshold value.
• the first flyback AC/DC converter stage 103 is enabled, and the second, third and fourth flyback AC/DC converter stages 104-106 are disabled.
• the output power provided to the light source 102 is between 0W and 50W.
• the first flyback AC/DC converter stage 103 is always enabled because the first flyback AC/DC converter stage 103 supplies electrical power not only over all levels of output power, but also supplies power to a controller (not shown in Figs. 1 and 2) for operation of all flyback AC/DC converter stages 103-106 of the driver circuit 101.
• the average sense voltage is above the threshold voltage associated with output power LEVEL1(203), and the first and second flyback AC/DC converter stages 103, 104 are enabled. With both the first and second flyback AC/DC converter stages 103, 104 enabled, the output power provided to the light source 102 in the present illustrative example is between 50W and 100W.
• the average sense voltage is above the threshold voltage associated with output power LEVEL2(204) and the first, second and third flyback AC/DC converter stages 103- 105 are enabled. With the first, second and third flyback AC/DC converter stages 103,104, 105 enabled, in the present illustrative example, the output power provided to the light source 102 is between 100W and 150W.
• the average sense voltage is above the threshold voltage associated with output power LEVEL3(205) and the first, second, third and fourth flyback AC/DC converter stages 103-106 are enabled.
• the output power provided to the light source 102 is between 150W and 200W.
• the number of flyback AC/DC converter stages 103-106 that are enabled is commensurately reduced. Notably, if the demand of output power remains above LEVEL3(205), the average sense voltage remains above the threshold voltage associated with output power LEVEL3(205), and none of the flyback AC/DC converter stages 103-106 is disabled.
• the average sense voltage is below the threshold voltage associated with LEVEL3(205)
• the fourth flyback AC/DC converter stage 106 is disabled, and the first, second and third flyback AC/DC converter stages 103-105 remain enabled.
• the average sense voltage is below the threshold voltage associated with output power LEVEL2(204)
• the third and fourth flyback AC/DC converter stages 105,106 are disabled, and the first and second flyback AC/DC converter stages 103-104 remain enabled.
• the second, third and fourth flyback AC/DC converter stages 104,105,106 are disabled, and the first flyback AC/DC converter stage 103 remains enabled. As noted above, regardless of the demand of output power, the first flyback AC/DC converter stage 103 remains enabled.
• FIG. 3 illustrates a simplified schematic diagram of a driver circuit 300 comprising parallel flyback converter stages in accordance with a representative embodiment.
• the driver circuit 300 may be implemented as driver circuit 101 described above.
• driver circuit 300 comprises four flyback AC/DC converter stages connected electrically in parallel. It is again emphasized that more or fewer than four flyback AC/DC converter stages may be connected electrically in parallel and implemented in the driver circuit 300 to provide more or fewer levels of output power in keeping with the present teachings.
• the dynamic range of output power of each of the flyback AC/DC converter stages is illustratively 0W to 50W, thereby providing a dynamic output power range for the driver circuit 300 of 0W to 200W.
• the dynamic output power range of each of the flyback AC/DC converter stages can be less than or greater than the illustrative range.
• the upper limit of the output power range of each flyback AC/DC converter stage is generally restrained by design considerations including the practical functional ranges of certain components thereof, such as switches and flyback transformers.
• the maximum output power of the driver circuit 300 can be increased by adding additional flyback AC/DC converter stages connected electrically in parallel.
• the driver circuit 300 comprises a first flyback AC/DC converter stage 301, a second flyback AC/DC converter stage 302, a third flyback AC/DC converter stage 303 and a fourth flyback AC/DC converter stage 304, all connected electrically in parallel.
• the first flyback AC/DC converter stage 301 comprises a controller 305.
• the first flyback AC/DC converter stage 301 also comprises a first switch 306, which is illustratively a MOSFET switch, and a sense resistor (Rs) 307 connected to the switch 306.
• the MOSFET is an n-MOSFET and the sense resistor (Rs) 307 is connected to the drain. If the MOSFET were a p-MOSFET, the sense resistor would be connected to the source.
• the sense voltage is equal to that average gate-to source voltage (V gs - aV g) of the MOSFET of the first flyback AC/DC converter stage 301 over a number of AC cycles.
• a threshold current can be compared to a sense current.
• the sense current is across the sense resistor, and thus is equal to an average current across the MOSFET (iMosFET-avg) of the first flyback AC/DC converter stage 301 over a number of AC cycles.
• sense resistor (R s ) 307 is merely illustrative, and other components for sensing the voltage or current across the switch of the first flyback AC/DC converter stage that are within the purview of one of ordinary skill in the art are contemplated.
• the power rating of the first switch 306 is comparatively low.
• the use of a MOSFET for a first flyback AC/DC converter stage 301 having an output power range of 0W to 50W requires the power rating and capacitance of the MOSFET to be comparatively low.
• the MOSFET of the first flyback AC/DC converter stage 301 has a voltage rating of approximately 500V and a current rating of 5A.
• no thermal management structure is required for such a MOSFET.
• known flyback AC/DC converters would require a MOSFET with an 800V voltage rating, a 20A current rating and a thermal management structure to provide an output power approaching 200W.
• the first flyback AC/DC converter stage 301 also comprises a first memory 308 and a second memory 309.
• the first memory 308 stores the sensed voltage levels (averaged over a fixed number of cycles) from the sense resistor (Rs) 307, and the second memory 309 stores the threshold voltage levels for each level of operation.
• the second memory 309 stores the threshold voltage levels for output power
• the threshold voltage levels stored in the second memory 309 are compared with the sense voltage levels to determine whether to enable or disable one or more of the second flyback AC/DC converter stage 302, the third flyback AC/DC converter stage 303 and the fourth flyback AC/DC converter stage 304.
• the controller 305 is a PFC controller such as an L6561 PFC controller or an L6562 PFC controller commercially available from ST Microelectronics.
• the first memory 308 and the second memory 309 are shown as separate memory elements for ease of description of the representative embodiments. Of course, the first memory 308 and the second memory 309 may be instantiated in the controller 305 or may be instantiated in other hardware or firmware (not shown) of the driver circuit 300.
• the first flyback AC/DC converter stage 301 also comprises a resistor-capacitor-diode (RCD) snubber circuit 310 and a flyback transformer 311.
• the RCD snubber circuit 310 controls the rate of rise of voltage on the drain of the first switch 306 of the first flyback AC/DC converter stage 301.
• the RCD snubber circuit 310 has a comparatively low power rating; and the flyback transformer 311 is a known flyback transformer that is comparatively small and exhibits commensurately low leakage inductance characteristics.
• the capacitor and resistor of the RCD snubber circuit 310 are comparatively small.
• a comparatively low voltage rectifier diode is provided in the RCD snubber circuit 310 because voltage "stress" is comparatively small.
• known RCD snubber circuits require a comparatively high voltage diode (e.g., a high voltage Zener diode).
• the second flyback AC/DC converter stage 302 comprises a second switch 312, which is also illustratively a MOSFET.
• the second flyback AC/DC converter stage 302 also comprises a gate controller 313.
• the gate controller 313 comprises a comparator that compares the sense voltage level stored in the first memory 308 with a first threshold voltage level (e.g., the threshold voltage associated with output power LEVEL1(203)) stored in the second memory 309. If the second switch 312 is not conducting, and the sense voltage level is greater than the first threshold voltage, the gate controller 313 turns the second switch 312 On' and the second flyback AC/DC converter stage 302 is enabled.
• a first threshold voltage level e.g., the threshold voltage associated with output power LEVEL1(203)
• the gate controller 313 turns the second switch 312 'off and the second flyback AC/DC converter stage 302 is disabled.
• the gate controller 313 does not turn the second switch 312 'on' and the second flyback AC/DC converter stage 302 remains disabled.
• the second flyback AC/DC converter stage 302 also comprises a RCD snubber circuit 314 and a flyback transformer 315.
• the RCD snubber circuit 314 and the flyback transformer 315 are substantially identical to the RCD snubber circuit 310 and the flyback transformer 311 described above.
• the third flyback AC/DC converter stage 303 comprises a third switch 316, which is also illustratively a MOSFET.
• the third flyback AC/DC converter stage 303 also comprises a gate controller 317.
• the gate controller 317 comprises a comparator that compares the sense voltage level stored in the first memory 308 with a second threshold voltage level (e.g., the threshold voltage of associated with output power LEVEL2(204)) stored in the second memory 309.
• the gate controller 317 turns the third switch 316 On' and the third flyback AC/DC converter stage 303 is enabled.
• the gate controller 317 turns the third switch 316 'off and the third flyback AC/DC converter stage 303 is disabled.
• the gate controller 317 does not turn the third switch 316 On' and the third flyback AC/DC converter stage 303 remains disabled.
• the third flyback AC/DC converter stage 303 also comprises a RCD snubber circuit 318 and a flyback transformer 319.
• the RCD snubber circuit 318 and the flyback transformer 319 are substantially identical to the RCD snubber circuit 310 and the flyback transformer 311 described above.
• the fourth flyback AC/DC converter stage 304 comprises a fourth switch 320, which is also illustratively a MOSFET.
• the fourth flyback AC/DC converter stage 304 also comprises a gate controller 321.
• the gate controller 321 comprises a comparator that compares the sense voltage level stored in the first memory 308 with a third threshold voltage level (e.g., the threshold voltage associated with output power LEVEL3(205)) stored in the second memory 309. If the fourth switch 320 is not conducting, and the sense voltage level is greater than the third threshold voltage, the gate controller 321 turns the fourth switch 320 On' and the fourth flyback AC/DC converter stage 304 is enabled.
• the gate controller 321 turns the fourth switch 320 'off and the fourth flyback AC/DC converter stage 304 is disabled.
• the gate controller 321 does not turn the fourth switch 320 On' and the fourth flyback AC/DC converter stage 304 remains disabled.
• the fourth flyback AC/DC converter stage 304 also comprises a RCD snubber circuit 322 and a flyback transformer 323.
• the RCD snubber circuit 322 and the flyback transformer 323 are substantially identical to the RCD snubber circuit 310 and the flyback transformer 311 described above.
• a signal 324 is provided from the second memory 309 to the gate controller 313.
• the signal 324 includes the threshold voltage stored in the second memory 309 and the sense voltage level stored in the first memory 308.
• the gate controller 313 comprises a comparator adapted to compare the threshold voltage stored and the sense voltage level. Based on this comparison, the gate controller 313 turns the second switch 312 on, or off, or makes no change to the current operating state of the second switch 312.
• a signal 325 is provided from the second memory 309 to the gate controller 317.
• the signal 325 includes the threshold voltage stored in the second memory 309 and the sense voltage level stored in the first memory 308.
• the gate controller 317 comprises a comparator adapted to compare the threshold voltage stored and the sense voltage level. Based on this comparison, the gate controller 317 turns the third switch 316 on, or off, or makes no change to the current operating state of the third switch 316.
• a signal 326 is provided from the second memory 309 to the gate controller 321.
• the signal 325 includes the threshold voltage stored in the second memory 309 and the sense voltage level stored in the first memory 308.
• the gate controller 321 comprises a comparator adapted to compare the threshold voltage stored and the sense voltage level. Based on this comparison, the gate controller 321 turns the fourth switch 320 on, or off, or makes no change to the current operating state of the fourth switch 320.
• an input AC signal 327 is provided as a DC output 328 after initial rectification by a bridge rectifier 329.
• Fig. 4 illustrates graphs of output power versus time (curve 401), feedback voltage (Vfb) versus time (curve 402), average sense voltage across a sense resistor (curve 403), gate-to- source (Vgs) across a second MOSFET versus time (curve 404), Vgs across a third MOSFET versus time (curve 405), and Vgs across a fourth MOSFET versus time (curve 406) in accordance with a representative embodiment.
• the output power increases over a number of cycles of AC input and with time.
• the threshold V t h (shown in curve 403) is at a level that will require all four flyback AC/DC converter stages 301-304 to be enabled.
• the demand for power at the DC output 328 is at its highest level (e.g., LEVEL 3 (205) in the example of Fig. 2).
• the sense voltage which is the voltage across the sense resistor (R s ) 307 (and thus across the first switch 306) averaged over a number of AC cycles, is above the threshold voltage.
• the threshold voltage which is stored in the second memory 309, is compared by the gate controller 313 of the second flyback AC/DC converter stage 302 to the sense voltage, which is stored in the first memory 308.
• the sense voltage is greater than the threshold voltage
• the demand for DC output power is greater than that which is supplied by the first flyback AC/DC converter stage 301 alone, and the gate controller 313 enables the second flyback AC/DC converter stage 302 as shown at 409 in curve 404.
• the sense voltage at 408 remains greater than the threshold voltage, and as such, activating the first and second flyback AC/DC converter stages 301, 302, while increasing the output power, has not resulted in the threshold voltage's being met and thus has not resulted in suitable output DC power at the DC output 328.
• the threshold voltage which is stored in the second memory 309, is compared by the gate controller 317 of the third flyback AC/DC converter stage 303 to the sense voltage, which is stored in the first memory 308. Because the sense voltage is still greater than the threshold voltage, the demand for DC output power is greater than that which is supplied by the first flyback AC/DC converter stage 301 and the second flyback AC/DC converter stage 302, and the gate controller 317 enables the third flyback AC/DC converter stage 303 as shown at 411 in cu rve 405. This results in a decrease in the sense voltage as shown at 410 in curve 403.
• the sense voltage at 410 remains greater than the threshold voltage, and as such, activating the first, second and third flyback AC/DC converter stages 301, 302,303, while increasing the output power, has not resulted in the threshold voltage's being met and thus has not resulted in suitable output DC power at the DC output 328.
• the threshold voltage which is stored in the second memory 309, is compared by the gate controller 321 of the fou rth flyback AC/DC converter stage 304 to the sense voltage, which is stored in the first memory 308. Because the sense voltage is still greater than the threshold voltage, the demand for DC output power is greater than that which is supplied by the first, second and third flyback AC/DC converter stages 301, 302, 303, the gate controller 321 enables the fourth flyback AC/DC converter stage 304 as shown at 413 in curve 406. This results in a decrease in the sense voltage as shown at 412 in curve 403.
• the sense voltage is slightly less than the th reshold voltage, and as such, activating the first, second, third and fourth AC/DC converter stages 301, 302, 303, 304, while increasing the output power, has resulted in the DC output power at the DC output 328 being equal to the demand.
• the feedback voltage reaches its operating point indicating that the output power equals the demand.
• Fig. 5 illustrates graphs of output power versus time (curve 501), feedback voltage versus time (Vfb) (curve 502), average sense voltage across a sense resistor (curve 503), gate-to- source (Vgs) across a second MOSFET versus time (curve 504), Vgs across a third MOSFET versus time (curve 505), and Vgs across a fourth MOSFET versus time (curve 506) in accordance with a representative embodiment.
• the output power decreases over a number of cycles of AC inpi and with time.
• the threshold V th (shown in curve 503) is at a level that will require only the first flyback AC/DC converter stage 301 to be enabled. As such, the demand for power at the DC output 328 is at its lowest level (e.g., below LEVEL 1 (203) in the example of Fig. 2).
• the sense voltage which is the voltage across the sense resistor (R s ) 307 (and thus across the first switch 306) averaged over a number of AC cycles, is below the threshold voltage.
• the driver circuit 300 is fully engaged and operating above LEVEL 3 (205) of Fig. 2.
• the sense voltage at 507 is below the threshold voltage, fewer flyback AC/DC converter stage(s) are required to be enabled to provide the desired output voltage. Thus, one or more flyback AC/DC converter stages will need to be disabled.
• the threshold voltage which is stored in the second memory 309, is compared by the gate controller 321 of the fourth flyback AC/DC converter stage 304 to the sense voltage, whic is stored in the first memory 308. Because the sense voltage is less than the threshold voltage the demand for DC output power is less than that which is supplied by the first through fourth flyback AC/DC converter stages 301-304. Accordingly, the gate controller 321 disables the fourth switch 320 and as a result disables the fourth flyback AC/DC converter stage 304 as shown at 508 in curve 506. This results in a decrease in the sense voltage as shown at 509 in curve 503.
• the sense voltage at 509 remains less than the threshold voltage, and as such, disabling the fourth flyback AC/DC converter stage 304, while decreasing the output power at the DC output 328, has not resulted in the threshold voltage's being met and thus ha not resulted in suitable output DC power at the DC output 328.
• the threshold voltage which is stored in the second memory 309, is compared by the gate controller 317 of the third flyback AC/DC converter stage 303 to the sense voltage, which is stored in the first memory 308. Because the sense voltage is still lower than the threshold voltage, the demand for DC output power is less than that which is supplied by the first, secon and third flyback AC/DC converter stages 301-303, and the gate controller 317 disables the third switch 316 and, thus the third AC/DC converter stage 303 as shown at 510 in curve 505. This results in an increase in the sense voltage as shown at 511 in curve 503.
• the sense voltage at 511 remains less than the threshold voltage, and as such, disabling the third and fourth flyback AC/DC converter stages 303, 304, while decreasing the output power, has not resulted in the threshold voltage's being met and thus has not resulted in suitable output DC power at the DC output 328.
• the threshold voltage which is stored in the second memory 309, is compared by the gate controller 313 of the third flyback AC/DC converter stage 303 to the sense voltage, which is stored in the first memory 308. Because the sense voltage is still lower than the threshold voltage, the demand for DC output power is less than that which is supplied by the first and second flyback AC/DC converter stages 301-302, and the gate controller 313 disables the second switch 312 and as a result, disables the second flyback AC/DC converter stage 302 as shown at 512 in curve 504. This results in a decrease in the sense voltage as shown at 513 in curve 503.
• the sense voltage is slightly less than the threshold voltage. Accordingly, the output DC power at the DC output 328 is at an appropriate level for the demand of the light source. Notably, the sense voltage can be exactly equal to the threshold voltage, indicating that the DC output exactly equals the demand by the light source.
• Fig. 6 illustrates a flow-diagram of a method 600 of driving a light source in accordance with a representative embodiment.
• the method 600 may be implemented in hardware and software such as described in connection with the representative embodiments of Figs. 1-5. Many of the details described in connection with representative embodiments of Figs. 1-5 are common to the presently described method, and generally are not repeated to avoid obscuring the description of the representative embodiments.
• the method 600 comprises sensing a voltage over a sense resistor in a first flyback AC/DC converter stage. At 602, the method 600 comprises comparing the voltage to a threshold voltage. At 603, the method 600 comprises enabling a second flyback AC/DC converter stage if the voltage is greater than the threshold voltage.
• the method 600 may be continued to enable more flyback AC/DC converter stages of the driver circuit (e.g., driver circuit 300) as needed to provide the requisite output power. Moreover, after attaining a desired output power, the method 600 may be 'reversed' to reduce the output power by disabling flyback AC/DC converter stages of the driver circuit.
• the driver circuit e.g., driver circuit 300
• inventive embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed.
• inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein.
• a reference to "A and/or B", when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

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• Circuit Arrangement For Electric Light Sources In General (AREA)
• Dc-Dc Converters (AREA)

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• 2011
  • 2011-07-22 EP EP11748469.1A patent/EP2609789B1/de not_active Not-in-force
  • 2011-07-22 JP JP2013525380A patent/JP5795803B2/ja not_active Expired - Fee Related
  • 2011-07-22 CN CN201180040933.8A patent/CN103069923B/zh not_active Expired - Fee Related
  • 2011-07-22 WO PCT/IB2011/053279 patent/WO2012025844A1/en active Application Filing
  • 2011-07-22 US US13/816,259 patent/US20130140999A1/en not_active Abandoned
  • 2011-07-22 BR BR112013004079A patent/BR112013004079A8/pt not_active Application Discontinuation

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